The “Big Ditch” project: Trans‐Atlantic mushroom disjunction tested using multiple taxonomic tools

Written descriptions and illustrations by historical Euro-Scandinavian mycologists crossed the Atlantic to America, where they were matched to fungi of the New World. Doubts about the accuracy of name applications across the ocean have persisted, but molecular phylogenies now provide a new level of resolution. Our research targets fleshy fungi whose names originated in Europe, but which bear the same name and superficial form in eastern North America. Several examples can be identified in which DNA sequences reveal differences across the ocean, including saprophytic (Marasmius rotula; Baeospora myosura; Sparassis crispa) and ectomycorrhizal (Strobilomyces strobilaceus; Tricholoma populinum) fungi. In addition, it appears that genes for sexual compatibility and recognition are more highly conserved than the internally transcribed spacer (ITS), but morphological differences vary with the individual taxon. Implications of this research include the necessity for new names for heretofore cryptic taxa on both continents and resultant adjustment of biodiversity inventory reports.